Mold for molding optical element

ABSTRACT

A mold for press molding an optical element of glass has carbon atoms injected in amounts from 1015 to 1018 ion/cm2 into a molding surface of a mold base of the mold and subjected to further treatment to form on the molding surface a diamond film, a hydrogenated amorphous carbon film, a hard carbon film or a mixture of at least two such films. The film on the molding surface can be formed by heat treatment and, additionally, by irradiation with hydrogen plasma, after carbon ion injection.

This application is a continuation of application Ser. No. 08/070,060filed Jun. 2, 1993, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mold for producing a glass opticalelement such as a lens or a prism by press molding of a glass material.

2. Related Background Art

The lens production technology using press molding of glass materialwithout a polishing process has enabled simple and inexpensiveproduction of lenses, without relying on the complex steps required inthe conventional technology, and has recently been employed not only inthe production of lenses but also prisms and other glass opticalelements.

The properties required for the mold employed in such press molding ofthe glass optical elements include excellent hardness, heat resistance,releasing property and mirror smoothness. For the material constitutingsuch mold, there have been various proposals including metals, ceramicsand materials coated therewith. For example, the Japanese PatentLaid-open Application No. 49-51112 proposes 13Cr martensite steel, theJapanese Patent Laid-open Application No. 52-45613 proposes SiC and Si₃N₄, the Japanese Patent Laid-open Application No. 60-246230 proposes anultra hard alloy coated with a precious metal, the Japanese PatentLaid-open Application Nos. 61-183134, 61-281030 and 1-301864 propose athin diamond film or a diamond-state carbon film, and the JapanesePatent Laid-open Application No. 64-83529 proposes a material coatedwith a hard carbon film.

However, 13Cr martensite steel has the drawbacks of being easilyoxidized, and coloration of the glass due to Fe diffusion therein at ahigh temperature. SiC and Si₃ N₄ are generally regarded as not beingoxidized, but are still oxidized at a high temperature, thus forming aSiO₂ film on the surface and causing glass fusion thereto. Also, theyhave a drawback that the shaping of the mold itself is extremelydifficult because of the high hardness. The material coated with theprecious metal does not easily cause glass fusion, but is easily damagedor deformed because it is extremely soft.

The mold employing the diamond thin film, the diamond-like carbon (DLC)film, the hydrogenated amorphous carbon (a-C:H) film or the hard carbonfilm shows satisfactory separation between the mold and the glass anddoes not cause glass fusion, but may result in an unsatisfactory moldingperformance due to the partial peeling of such film, after severalhundred molding operations. These reasons are considered as follows:

(1) The above-mentioned films have a very large compression stress, andare peeled or cracked as a result of the stress release, caused by therapid heating and rapid cooling in the molding process. Similarphenomena result from the thermal stress caused by the thermal cyclesand the difference in the thermal expansion coefficients of the basematerial and the film constituting the mold; (2) In certain basematerials of the mold, the film may not be formed locally or may belocally thinner depending on the surface state. For example, in asintered material of WC--Co, SiC or Si₃ N₄, voids of particles or poresin sintering are unavoidable, so that the polished surface containsholes of several microns or larger. If a film is formed on such surface,it may not be formed or may become extremely thin in such holes.Consequently, such locations may induce formation of peeling or cracksince the adhesion strength or mechanical strength of the film becomeextremely low in such locations; (3) The sintering material in thesintered material, as represented by Co in WC--Co, forms an alloy bydiffusion with said film. Such portion causes glass fusion in themolding operation, thus generating a precipitate by reaction with theglass components and deteriorating the durability of the mold.

As explained above, the mold for optical elements, excellent in moldingproperty, durability and economical property has not been realized.

SUMMARY OF THE INVENTION

A first invention resolves the above-mentioned drawbacks by a moldprovided with an area, at the interface between a mold base of the moldand a carbon film formed on the molding surface of the mold base, inwhich an element constituting the mold base and an element constitutingthe film are combined with oxygen.

Carbon has been employed in the mold for molding glass, because glass isnot well compatible with carbon. In glass molding to be performed withmore precision, the hard and smooth carbon film is formed on the moldingsurface of the mold base of the mold. However, since such film has ahigh internal stress and lacks thermal stability in the high temperaturerange for glass molding, the adhesion strength between the mold base andthe film is reduced with the number of molding operations. Stateddifferently, the drawback of the carbon film, as the surface materialfor the glass mold is principally related to the adhesion strengthbetween the mold base and the film.

This drawback can be prevented in the present invention by the formationof a carbon film such as a diamond film, a DLC film, an a-C:H film or ahard carbon film on the molding surface of the mold base of the mold byforming an area containing oxygen bonded to the mold base and the carbonfilm in order to improve the adhesion strength of the mold base and thefilm. The oxygen-containing area does not constitute the spontaneousoxide film ordinarily present on the surface of the mold base, but isformed after elimination of the spontaneous oxide film. Oxygen is bondedat the base material side to a constituent element thereof, and at thecarbon film side to oxygen and/or hydrogen. Such interface containingsuch oxygen atoms can be formed at the formation of the carbon film byirradiating an oxygen ion beam or oxygen plasma, or employing a materialcontaining oxygen in the initial stage of carbon film formation, oreffecting a heat process in an atmosphere containing a suitable amountof oxygen after the formation of the carbon film. The amount of oxygenin the interface is generally in a range of 1-10 atom. %, because anoxygen amount exceeding 10 atom. % deteriorates the adhesion strengthbetween the mold base and the film, while an amount less than 1 atom. %does not improve the adhesion strength. Also, the thickness of theoxygen-containing interface is generally in a range of 5-500 Å, becausea thickness exceeding 500 Å not only deteriorates the adhesion strengthof the mold base and the film but also deteriorates the hardness of thefilm, while a thickness less than 5 Å does not improve the adhesionstrength.

In the present invention, a material used for the mold base is selectedfrom the group consisting of WC, SiC, TiC, TaC, BN, TiN, AlN, Si₃ N₄,SiO₂, Al₂ O₃, ZrO₂, W, Ta, Mo, thermet, thialon, mulite, carboncomposite (C/C), carbon fibers (CF) and WC--Co alloy. Theabove-mentioned carbon film is formed on the molding surface of suchmold base. The diamond film is formed by microwave plasma CVD, thermalfilament CVD, plasma jet or electron cyclotron resonance plasma CVD.Also, the DLC film, a-C:H film or hard carbon film is formed, forexample, by plasma CVD, ion beam sputtering, ion beam evaporation ofplasma sputtering. Examples of the gas employed for film formationinclude hydrocarbons such as methane, ethane, propane, ethylene, benzeneor acetylene; halogenated hydrocarbons such as methylene chloride,carbon tetrachloride, chloroform or trichloroethane; alcohols such asmethyl alcohol or ethyl alcohol; ketones such as (CH₃)₂ CO or (C₆ H₅)₂CO; gasses such as CO or CO₂ ; and mixtures of the gasses with othergasses such as N₂, H₂, O₂, H₂ O or Ar.

As explained above, the first invention provides a mold having, at theinterface between the mold base of the mold and the carbon film such asthe diamond film, DLC film, a-C:H film or hard carbon film formed on themolding surface of the mold base, an area in which the constituentelement of the mold base material and that of the film are bonded withoxygen, thereby improving the adhesion strength between the mold baseand the film and improving the durability of the mold.

A second invention prevents the above-mentioned drawbacks by a mold inwhich carbon ions are introduced into the molding surface of the moldbase of the mold by ion injection or ion implantation, or a mold inwhich a carbon film is formed after carbon ion introduction.

The ion injection or implantation is a technology for forming asurfacial layer of certain properties different from those of the bulkmaterial by ionizing the particles to be implanted and accelerating theparticles toward a solid substrate by a voltage of several 10 keV toseveral 100 keV in ultra high vacuum. The ions penetrating the solidlose energy by repeated collisions with the atoms constituting thesubstrate. As a result, the implanted ions remain in the solidsubstrate, and the penetration depth in ordinary ion implantation isabout 0.01 to 1 μm. The distribution of the implanted ions in the solidcan be determined by LSS theory for most ions and most solids in casethe solid is amorphous. Also, the depth and spreading of the maximumconcentration are determined by the substrate, the implanted ions andthe acceleration energy thereof.

The present invention can resolve the aforementioned drawback in theadhesion strength between the mold material of the mold and the carbonfilm by forming an injected-carbon layer on the surfacial part of themolding surface by means of injection of carbon ions into the moldingsurface. The injected layer shows satisfactory adhesion to the moldbase, a surface hardness at least comparable to that of the mold base,and satisfactory thermal stability at the high temperature. The amountof injection is preferably in a range of 10¹⁵ to 10¹⁸ ions/cm², becausean amount less than 10¹⁵ ions/cm² results in unsatisfactory releasingproperty from glass, while an amount exceeding 10¹⁸ ions/cm²deteriorates the surface state because the molding surface is sputtered.Then, a heat treatment of the mold base during or after the injectionspreads the distribution by acceleration and diffusion of the injectedions, thus realizing a deep penetration. As a result, the adhesion tothe mold base is further improved, and the thermal stability isimproved.

When the carbon film is formed on the molding surface subjected to theinjection of carbon ions, the adhesion of the mold base and the film isimproved in comparison with the case without the ion injection. Theadhesion between the mold base and the film can be further improved byirradiating the injected surface with hydrogen plasma for eliminatingthe surfacial amorphous (graphite) portion in the ion-injected layerprior to the formation of the carbon film. In such case the lower limitof the amount of the injected ions may be less than 10¹⁵ ion/cm². Thecarbon film formed on the ion-injected molding surface is a diamondfilm, an a-C:H film, a DLC film, a hard carbon film, or a filmconsisting of a mixture of at least two thereof. The mold base, themethod for forming these films, and the examples of the gas to beemployed are same as explained before.

As explained above, the second invention improves the adhesion strengthbetween the mold base of the mold and the film by injecting carbon ionsinto the molding surface of the mold base or by forming a carbon filmsuch as a diamond film, a DLC film, an a-C:H film or a hard carbon filmafter said ion injection, thereby improving the durability of the mold.

A third invention prevents the above-mentioned draw backs by a moldsubjected to ion injection during or after formation of a carbon film onthe molding surface of the mold base of the mold.

During or after formation of a carbon film such a diamond film, a DLCfilm, an a-C:H film or a hard carbon film on the molding surface of thebase material of the mold, high energy ions having a flying strokelarger than the interface of the film are injected preferably with aconcentration of 10¹⁴ ion/cm² or higher, thereby mixing the atoms of themold base and the film at the interface. The beam mixing is used formixing the atoms at the interface of the base material and the film,thereby eliminating the sharp interface or forming a compound by atommixing.

When a solid substrate is irradiated with an ion beam of several keV orhigher, the surfacial layer of the substrate is scraped by sputtering,while the irradiating ions penetrates the surfacial part of thesubstrate. The penetrating ions collide with the atoms of the solidsubstrate, thereby losing energy, and are eventually stopped. Thecollision may occur in nuclear mode or in electronic mode. The formercauses extraction of the substrate atoms while the latter causesexcitation. These phenomena can cause a structural change, and the ionbeam irradiation can vary the composition or structure of the surfacelayer of the solid substrate, thereby modifying the surfacial layer alsoin macroscopic manner. Also, the ion irradiation on a thin filmprovides, under a condition that the ion beam passes the interface ofthe thin film and the base material, an effect of causing the atommixing in the vicinity of the interface, not only in the direction ofdepth but also in a direction perpendicular to the incident direction ofthe ion beam. The irradiating ions, upon entering the solid substrate,lose energy by repeated collisions with the atoms of the solid and areeventually stopped in the solid substrate. The depth of penetration isabout 0.01 to 1 μm in the ordinary ion injection. The distribution ofthe implanted ions in the solid is determined by LSS theory for mostions and most solids in case the solid is amorphous. Also the depth andspreading of the maximum concentration are determined by the substrate,the implanted ions and the energy thereof.

The present invent ion can resolve the aforementioned drawback in theadhesion strength between the mold base of the mold and the carbon film,by injecting ions of a high energy having a flying stroke larger thanthe interface of the carbon film, thereby causing atom mixing at theinterface between the molding surface and the film during or afterformation of a carbon film which is not compatible with glass, such as adiamond film, a DLC film, an a-C:H film or a hard carbon film, on themolding surface of the mold base. An injected amount of ions at leastequal to 10¹⁴ ion/cm² can provide a sufficient mixing effect at theinterface between the mold base and the film. However, a range of 10¹⁴to 10¹⁸ ion/cm² is preferred as long as possible because an amountexceeding 10¹⁸ ion/cm² may crease a coarse surface. A heat treatmentduring or after the mixing spreads the distribution by acceleration anddiffusion of the ions, thereby attaining a deeper penetration andimproving the mixing effect. As a result, the adhesion to the mold baseis further improved, and the thermal stability is also improved. Thecarbon film formed on the molding surface subjected to the ionimplantation can be a diamond film, a DLC film, an a-C:H film or a hardcarbon film, or a film of a mixture of at least two thereof. The moldbase, the method for film formation and the examples of the gas to beemployed are same as explained before.

As explained above, the third invention improves the adhesion strengthbetween the mold base of the mold and the film by ion injection duringor after the formation of a carbon film such as a diamond film, a DLCfilm, an a-C:H film or a hard carbon film on the molding surface of themold base, thereby improving the durability of the mold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of the mold foroptical element of the present invention prior to press molding;

FIG. 2 is a cross-sectional view of an embodiment of the mold foroptical element of the present invention after press molding;

FIG. 3 is a schematic view of an ECR plasma CVD apparatus employed inthe embodiment of the present invention;

FIG. 4 is a cross-sectional view of a non-continuous lens moldingapparatus employing the mold for optical element of the presentinvention;

FIG. 5 is a chart of the time-temperature relationship in lens molding;

FIG. 6 is a cross-sectional view of a continuous lens molding apparatusemploying the mold for optical element of the present invention;

FIG. 7 is a schematic view of a polishing apparatus employed in theembodiment of the present invention;

FIG. 8 is a schematic view of an IBD apparatus employed in theembodiment of the present invention;

FIG. 9 is a schematic view of a convection oven employed in theembodiment of the present invention;

FIG. 10 is a schematic view of a sputtering apparatus employed in theembodiment of the present invention;

FIG. 11 is a schematic view of a microwave plasma CVD apparatus employedin the embodiment of the present invention;

FIG. 12 is a schematic view of composite IBD apparatus employed in theembodiment of the present invention;

FIG. 13 is a schematic view of an ion beam sputtering apparatus employedin the embodiment of the present invention; and

FIG. 14 is a schematic view of a composite IBD apparatus employed in theembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be explained in detail by preferredembodiments thereof with reference to the attached drawings.

Embodiment having oxygen atoms at the interface of carbon film and basematerial of the mold (Examples 1-6)!

(EXAMPLE 1)

FIGS. 1 and 2 illustrate an embodiment of the mold for optical element,of the present invention. FIG. 1 shows the state of press moldingsurfaces for the optical element. FIG. 2 shows a state after pressmolding. There are shown a mold base 1, a DLC film 2 having a moldingsurface for producing the optical element, a glass material 3, and anoptical element 4. The optical element 4 such as a lens is formed bypress molding the glass material 3 placed between the mold members asshown in FIG. 1.

In the following there will be given a detailed explanation on the moldof the present invention, for producing the optical element.

The base material of the mold was formed by working sintered SiC into apredetermined shape, then forming a polycrystalline SiC film by CVD, andmirror polishing the molding surface. After sufficient washing, the moldbase was placed in an ECR plasma CVD apparatus shown in FIG. 3, in whichthere are illustrated a plasma generating chamber 5, a mold 6, a gassupply system 7, a microwave oscillator 8 with a wave guide, anevacuating system 9, and a sample holder 10. After the apparatus wasevacuated to 1×10⁻⁶ Torr, argon was supplied at 50 sccm from gas supplysystem to a pressure of 2×10⁻² Torr. Then, microwave of 2.45 GHz wasapplied by the oscillator 8 with a power of 500 W, thereby effecting acleaning process for eliminating the surfacial oxide film by about 350 Åwith argon plasma. Then oxygen was introduced at 50 sccm from the gassupply system with a pressure of 3×10⁻² Torr. Microwave of 2.45 GHz wasapplied with a power of 700 W to form ECR oxygen plasma for irradiatingthe surface of the base material for 2 minutes. Further, C₆ H₆ wascharged at 25 sccm from the gas supply system at a pressure of 2×10⁻³Torr, and microwave of 2.45 GHz was applied by the oscillator 8 with apower of 500 W. At the same time an external electromagnet 12 applied adiverging magnetic field of 1500 Gauss at a microwave introductionwindow 11, 875 Gauss at the exit of the plasma chamber, and 650 Gauss atthe position of the base. Also, a negative bias of -500 V was applied tothe base by a bias source (not shown) to form a DLC film of a thicknessof 2000 Å. In this operation the base was heated to 300° C.

There will be explained an example of press molding of glass lenses withthe mold of the present invention. In FIG. 4, there are shown a vacuumtank 51, a cover 52 thereof, an upper mold 53 for forming the opticalelement, a lower mold 54, a support member 55 for the upper mold, acylindrical mold 56, a mold holder 57, a heater 58, a push-up rod 59 forthe lower mold, an air cylinder 60 for driving the push-up rod, an oilrotary pump 61, valves 62, 63, 64, an inert gas pipe 65, a valve 66, aleak valve 67, a valve 68, a temperature sensor 69, a cooling water pipe70, and a table 71 supporting the vacuum tank.

The lens producing process will be explained in the following.

A spherical glass material consisting of a predetermined amount of flintoptical glass (SF14), is placed in the cavity of the mold members, whichare then placed in the molding apparatus. Subsequently, the cover 52 ofthe vacuum tank 51 is closed, then water is supplied in the coolingwater pipe 70, and the heater 58 is powered. In this state the nitrogenvalves 66, 68 are closed, and the evacuating valves 62, 63, 64 are alsoclosed. The oil rotary pump 61 is continuously operated. The valve 62 isopened to start evaluation, and is closed when the pressure reaches 10⁻²Torr or lower. Then, the valve 66 is opened to introduce nitrogen intothe vacuum tank from a container. When a predetermined temperature isreached, the air cylinder 60 is activated to effect pressurization for 1minute at 200 kg/cm². After the pressure is released, the cooling isconducted with a rate of -5° C./min to a temperature below thetransition point, and is then continued with a rate of -20° C./min orhigher. When the temperature becomes 200° C. or lower, the valve 66 isclosed, and the leak valve 63 is opened to introduce air into the vacuumtank 51. Then, the cover 52 is removed, the upper mold support isremoved, and the molded article is taken out. A lens 4 shown in FIG. 2was molded in the above-explained manner with the flint optical glassSF14 (softening point Sp=586° C.; transition temperature Tg=485° C.).FIG. 5 shows the molding conditions, or the time-temperaturerelationship in this process.

The above-explained mold was used in molding operations three hundreds(300) times. In the observations under an optical microscope or ascanning electron microscope (SEM), the mold after the moldingoperations did not show defects such as scar or crack, nor Pbprecipitation resulting from reduction of PbO contained in the glass norglass fusion. Also the molded article was satisfactory in the surfaceroughness, surface accuracy, transmittance and precision of the shape,and was free from Pb precipitation or gas preservation at the moldingoperation.

Then, the mold was used in the molding operation with a moldingapparatus shown in FIG. 6.

In FIG. 6 there are shown a molding apparatus 102, an intake replacementchamber 104, a molding chamber 106, an evaporation chamber 108, atake-out replacement chamber 110, gate valves 112, 114, 116, rails 118,a palette 120 moved in a direction A on the rails, cylinders 124, 138,140, 150, valves 126, 152, and heaters 128 provided along the rails 118in the molding chamber 106.

The molding chamber 106 is divided, into a heating zone 106-1, apressing zone 106-2 and an annealing zone 106-3, along the transportingdirection of the palette. In the pressing zone 106-2, an upper mold 130is fixed to the lower end of a rod 134 of said cylinder 138, and a lowermold 132 is fixed to the upper end of a rod 136 of the cylinder 140. Theupper and lower molds 130, 132 are the molds of the present invention.In the evaporation chamber 108, there are provided a container 142containing an evaporation material 146, and a heater 144 for heating thecontainer.

A blank for molding was prepared by rough working of crown glass SK12(softening point Sp=672° C.; glass transition temperature Tg=550° C.)into predetermined shape and dimension. The glass blank was placed onthe palette 120. The palette was placed at a position 120-1 in theintake replacement chamber 104, and was pushed in the direction A by arod 122 of the cylinder 124 to a position 120-2 in the molding chamber106 across the gate valve 112. Subsequently, the palettes wereintroduced in succession at predetermined timings into the replacementchamber 104, and were transported from the position 120-2 to 120-8 inthe molding chamber 106. During the transportation, the glass blank wasgradually heated by the heaters 128 in the heating zone 106-1, broughtto a temperature exceeding the softening point in the position 120-4,and brought to the pressing zone 160-2. The cylinders 138, 140 wereactivated to effect the pressing operation with the upper and lowermolds for 1 minute at a pressing temperature of 620° C. with a pressureof 200 kg/cm². Thereafter, the pressure was released, then cooling wasconducted to a temperature below the glass transition point, and thecylinders 138, 140 were operated to release the upper and lower moldsfrom the molded glass. In the pressing operation, the palette wasutilized as a cylindrical mold. Thereafter, the molded glass wasgradually cooled in the annealing zone 106-3. The molding chamber 106was filled with inert gas. The palette having reached the position 120-8in the molding chamber 106 was transported then to a position 120-9 inthe evaporation chamber 108 across the gate valve 114. There is usuallyvacuum evaporation conducted, which was omitted in this example.Subsequently, the molded glass was transported to a position 120-11 inthe replacement chamber 110 across the gate valve 116. Then, the moldedglass was taken out from the molding apparatus by a rod 148 of thecylinder 150.

After molding operations three thousands (3000) times as explainedabove, the mold members showed satisfactory results in the moldingsurface state, the surface roughness of the molded optical element, andthe releasing property of the molds from the molded optical element. Inthe observations under an optical microscope and a SEM, the moldingsurface of the mold did not show defects such as scar or crack, nor Pbprecipitation nor glass fusion.

(EXAMPLE 2)

After sintered Si₃ N₄ was worked into a predetermined shape as a moldbase, it was subjected to a scarring process by ultrasonic vibration inalcohol containing diamond grinding particles of a diameter of 5-10 μmin order to increase the diamond nucleation density. After sufficientwashing, the mold base was placed in the film forming apparatus shown inFIG. 3, and was irradiated with oxygen plasma as in the example 1 aftersurface cleaning with argon ions. Then, CH₄ at 1.4 sccm and H₂ at 300sccm were supplied from the gas supply system with a pressure of 50Torr. Microwave of 2.45 GHz was applied with a power of 1000 W togenerate ECR plasma in the vicinity of the base. The mold base washeated to 800° C. to form a polycrystalline diamond film with athickness of 10 μm. Since the film was relatively rough (P-V=0.1 μm), itwas mirror polished to a surface roughness of R_(max) =0.02 μm withdiamond grinding particles in a polishing apparatus shown in FIG. 7. InFIG. 7 there are shown a mold 13, an air bearing 14, a polishing dish15, a bearing 16, an air bearing 17, a spring 18, and a motor 19. Thepolishing was conducted in an aspherical shape to the above-mentionedsurface roughness by local polishing with the polishing dish rotated at1000 rpm and positioned always in the normal direction to the surface tobe polished. The obtained mold was subjected to a molding test similarto that of the example 1 and provided results similar to those in theexample 1.

(EXAMPLE 3)

A mold base same as in the example 1 was subjected to the formation ofan a-C:H film by an IBD (ion beam deposition) apparatus which isschematically shown in FIG. 8, wherein shown are a vacuum tank 20, anion beam generator 21, an ionizing chamber 22, a gas inlet 23, an ionbeam extracting grid 24, an ion beam 25, a mold base material 26, asubstrate holder 27 with a heater, and an evacuating outlet 28. At firstargon was introduced at 30 sccm from the gas inlet into the ionizingchamber and was ionized, and a voltage of 450 V was applied to theextracting grid to obtain an ion beam for irradiating the mold base for5 minutes thereby cleaning the surface of the mold base. Then CH₄ at 15sccm and Ar at 30 sccm were introduced into the ionizing chamber, and ana-C:H film was formed with a thickness of 1500 Å, at a gas pressure of3×10⁻⁴ Torr. In this operation the mold base was heated to 300° C. Threemolds prepared under a same condition were heat treated in a furnaceshown in FIG. 9. After the furnace was evacuated to 5×10⁻⁶ Torr by anevacuating system 30, N₂ and O₂ were introduced from a gas inlet 31 to apressure of 1.2 atom with an O₂ partial pressure of 1×10⁻⁶ Torr. Moldswere prepared by heating the mold base 32 in an infrared furnace 33 for1 and 10 hours at 600° C., while another mold was prepared without suchheating. Films formed on CVD-SiC wafers under the same conditions wereevaluated. The ESCA analysis of the a-C:H film to the interface in thedirection of depth provided the oxygen distribution of the specimens asshown in Table 1. Also, the adhesion strength of the film evaluated by ascratch tester, in shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                                          Adhesion                                    Heat     O.sub.2 concentration                                                                       O.sub.2 present area                                                                     strength                                    treatment                                                                              (at. %)       (Å)    (mN)                                        ______________________________________                                        none     0              0         250                                          1 hour  5             300        600                                         10 hours 11            550        300                                         ______________________________________                                    

In a molding test similar to that in the example 1, the mold withoutheat treatment showed slight film peeling in the peripheral area after250 moldings while the mold heated for 10 hours showed similar peelingafter moldings one hundred and fifty (150) times, but the mold heatedfor 1 hour did not show defects such as film peeling even after moldingsthree hundreds (300) times.

(EXAMPLE 4)

Molds were prepared with the O₂ plasma irradiating time of 0, 10seconds, 5, 10 and 15 minutes at the preparation of the DLC film as inthe example 1, and CVD SiC wafers for evaluation were prepared in thesame manner. The evaluation samples were subjected to the ESCA surfaceanalysis and the evaluation of adhesion strength by the scratch tester.The obtained results are summarized in Table 2.

                  TABLE 2                                                         ______________________________________                                                                          Adhesion                                    O.sub.2 process                                                                        O.sub.2 concentration                                                                       O.sub.2 present area                                                                     strength                                    time     (at. %)       (Å)    (mN)                                        ______________________________________                                        0     sec.   0             0        250                                       10    sec.   1             5        300                                       5     min.   5             250      600                                       10    min.   10            500      550                                       15    min.   750           300                                                ______________________________________                                    

The ESCA analysis of the a-C:H film to the interface in the direction ofdepth provided the oxygen distribution shown in Table 2, which alsoincludes the result of evaluation of the adhesion strength of the filmby the scratch tester.

In a molding test similar to that of the example 1, the mold without theO₂ plasma irradiation and the mold subjected to the irradiation for 15minutes showed slight film peeling in the peripheral portion,respectively after moldings 250 and 100 times. However, the moldssubjected to said irradiation for 5 and 10 minutes did not show defectssuch as film peeling even after molding 300 times.

(EXAMPLE 5)

A mold base same as that in the example 1 was subjected to theelimination of the spontaneous oxide film at the surface by Ar reversesputtering in a sputtering apparatus shown in FIG. 10. Morespecifically, a vacuum tank 160 was evacuated to 1×10⁻⁶ Torr by anevacuating system 163, then Ar gas was introduced by a gas supply system162 to a pressure of 3×10⁻³ Torr. The mold base 161 was sputtered byapplying a high frequency voltage of 13.56 MHz by an RF power source164. Then, O₂ gas was introduced to a pressure of 4×10⁻³ Torr, and ahigh frequency voltage of 13.56 MHz was applied by the RF power source164 with a power of 700 W to generate O₂ plasma, to which the surface ofthe mold base was exposed for 5 minutes. Thereafter, sputtering wascontinued with a graphite target 165 of a purity of 99.99% utilizing Arplasma to form a hard carbon film of a thickness of 2000 Å on thesurface of the mold base. In this operation the base material was heatedto 300° C., and the sputtering was conducted with a gas pressure of4×10⁻³ Torr and an RF power density of 4 W/cm². A molding test similarto that in the example 1, employing thus obtained mold provided resultssimilar to those of the example 1.

(EXAMPLE 6)

A mold base was processed in the same manner as in the example 1, and aDLC film of a thickness of 2000 Å was formed by conducting the filmformation under the same conditions as in the example 1 for about 2minutes with O₂ being mixed at 5 sccm with C₆ H₆ and thereafter cuttingoff the supply of O₂. In a molding test similar to that of the example1, thus obtained mold provided the results similar to those of theexample 1.

Embodiment of carbon ion implantation or carbon ion implantationfollowed by carbon film formation (examples 7-13)!

(EXAMPLE 7)

FIGS. 1 and 2 also illustrate an embodiment of the mold of the presentinvention for optical element formation. FIG. 1 shows the state of thepress molding surface for the optical element while FIG. 2 shows a stateafter the molding. In this embodiment, a numeral 2 in FIG. 1 indicatesan ion implanted surface constituting the molding surface for theoptical element.

The mold of the present invention for the optical element will beexplained in detail in the following.

A mold base was prepared by working sintered SiC into a predeterminedshape, then forming a polycrystalline SiC film by CVD, andmirror-polishing the molding surface. After sufficient washing, the moldbase was subjected, in an ion implantation apparatus (not shown), to theimplantation of C⁺¹² obtained by mass separation onto the mold surfacewith an energy of 60 keV and a concentration of 6×10¹⁵ ion/cm². Thesurface roughness after the implantation was evaluated as R_(max) =0.03μm.

Thus obtained mold was used in a molding operation as in the example 1,utilizing the molding apparatus shown in FIG. 4. In the observationsunder an optical microscope and a scanning electron microscope (SEM),the mold after moldings 300 times did not show defects such as scars orcracks, nor Pb precipitation resulting from reduction of PbO containedin the glass, nor glass fusion. Also, the molded products weresatisfactory in the surface roughness, surface precision, transmittanceand shape precision, and were free from Pb precipitation or gasretention.

The mold was also employed in a molding operation utilizing the moldingapparatus of FIG. 6, in a similar manner as in the example 1. Even aftermoldings 3000 times, satisfactory results were observed in the state ofthe molding surface of the mold, the surface roughness of the moldedoptical element, and the releasing property of the mold from the moldedoptical element. Also, in the observations under an optical microscopeand a scanning electron microscope, the molding surface did not showdefects such as scars or cracks, nor Pb precipitation nor glass fusion.

(EXAMPLE 8)

A mold base was prepared by working a sintered material composed of WC(84%), Tic (8%) and Tac (8%) into a predetermined shape, andmirror-polishing the molding surface to R_(max) =0.02 μm. The mold basematerial was placed in the ion implantation apparatus (not shown) as inthe example 7, and was subjected to the implantation of C⁺¹³ obtained bymass separation with an energy of 90 keV and a concentration of 7×10¹⁵ion/cm². For the purpose of comparison, molds were prepared also withimplanting concentrations of 5×10¹⁴ and 3×10¹⁸ ion/cm², respectively.Each of these three molds was used in the molding apparatus shown inFIG. 4 for molding, as in the example 7, the flint optical glass SF14(softening point Sp=586° C.; transition temperature Tg=485° C.) 300times, and the obtained results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                             Amount of ion  Surface roughness                                                                         Mold release-                                 Mold implantation   of mold (R.sub.max)                                                                       ing property                                  ______________________________________                                        1    7 × 10.sup.15 ion/cm.sup.2                                                             ≦0.03 μm                                                                        satisfactory                                  2    5 × 10.sup.14 ion/cm.sup.2                                                             ≦0.03 μm                                                                        glass fusion                                  3    3 × 10.sup.18 ion/cm.sup.2                                                             ≧0.03 μm                                                                        satisfactory                                  ______________________________________                                    

In the observations under an optical microscope and a scanning electronmicroscope, the molds after the molding operations did not show, as inthe example 7, defects such as scars or cracks, nor Pb precipitationresulting from reduction of PbO contained in the glass, nor the glassfusion. Also, the molded products were satisfactory in the surfaceroughness, surface precision, transmittance and shape precision and werefree from Pb precipitation or gas retention.

(EXAMPLE 9)

A mold subjected to the ion implantation as in the example 7 wassubsequently heat treated at 800° C. A molding test as in the example 7,employing thus obtained mold provided results similar to those of theexample 7.

(EXAMPLE 10)

A mold base was obtained by forming sintered Si₃ N₄ into a predeterminedshape and mirror-polishing it to a surface roughness of R_(max) =0.03μm. Then, the molding surface was subjected to the implantation of C⁺¹²with a concentration of 5×10¹⁵ ion/cm², as in the example 7. Then, priorto the formation of a diamond film, the molding surface was subjected toa scarring treatment by ultrasonic vibration in alcohol in which diamondgrinding particles of a diameter of 5-10 μm were dispersed in order toincrease the diamond nucleation density. Then, after sufficient washing,the mold base was placed in a microwave CVD apparatus shown in FIG. 11,wherein shown are a plasma chamber 45, a mold 46, a gas supply system47, a microwave oscillator 48 with a wave guide, and an evacuatingsystem 49. At first the apparatus was evacuated to 1×10⁻⁶ Torr, then CH₄at 1.5 sccm and H₂ at 350 sccm were introduced from the gas supplysystem to a pressure of 55 Torr, and microwave of 2.45 GHz was appliedwith a power of 800 W. The mold base was heated to 850° C. to form apolycrystalline diamond film of a thickness of 15 μm thereon. Since thefilm had a relative rough surface of P-V=0.1 μm, it was mirror polishedto a surface roughness of R_(max) =0.02 μm with diamond grindingparticles in a polishing apparatus shown in FIG. 7. Polishing in anaspherical shape was attained by local polishing with a polishing dish,which was rotated at 1000 rpm and constantly directed perpendicularly tothe polished surface. A molding test as in the example 7, employing thusobtained mold, provided results similar to those in the example 7.

(EXAMPLE 11)

A mold base subjected to the ion implantation as in the example 9 andthen heat treated was subjected to the formation of an a-C:H film in anIBD (ion beam deposition) apparatus shown in FIG. 8, as employed in theexample 3. At first Ar was introduced at 30 sccm from the gas inlet intothe ionizing chamber and ionized. Then, an ion beam was extracted byapplying a voltage of 450 V to the extracting grid and was directed tothe mold base for 5 minutes, thereby cleaning the molding surface. Then,CH₄ at 20 sccm and Ar at 30 sccm were introduced into the ionizingchamber, and an a-C:H film of a thickness of 1000 Å was formed under agas pressure of 4×10⁻⁴ Torr. In this operation, the mold base was heatedat 300° C. A molding test as in the example 7, employing the thusobtained mold, provided results similar to those in the example 7.

(EXAMPLE 12)

A mold base as in the example 11 was subjected to the limitation of thesurfacial spontaneous oxide film by reverse Ar sputtering in thesputtering apparatus shown in FIG. 10. More specifically, after thevacuum tank 160 was evacuated to 1×10⁻⁶ Torr by means of the evacuatingsystem 163, Ar gas was introduced from the gas supply system 162 with apressure of 3×10⁻³ Torr and a high frequency voltage of 13.56 MHz wasapplied by the RF power source 164 to sputter the mold base. Thensputtering was continued employing a graphite target 165 of a purity of99.99% and Ar plasma to form a hard carbon film of a thickness of 2000 Åon the base material. In this operation, the mold base was heated to300° C., and the sputtering was conducted with a gas pressure of 4×10⁻³Torr and an applied RF power density of 5 W/cm². A molding test as inthe example 7, employing thus obtained mold, provided results similar tothose in the example 7.

(EXAMPLE 13)

After a mold base was processed as in the example 11, it was placed inthe ECR plasma CVD apparatus shown in FIG. 3. After the apparatus wasevacuated to 1×10⁻⁶ Torr, H₂ was supplied at 50 sccm from the gas supplysystem to a pressure of 2×10⁻⁶ Torr. Then microwave of 2.45 GHz wasapplied by the oscillator 8 with a power of 700 W, and the ion implantedmolding surface was irradiated with H₂ plasma of 0.1 mA/cm² for 10minutes. Then, C₆ H₆ was introduced at 30 sccm from the gas supplysystem with a pressure of 2.5×10⁻³ Torr, and microwave of 2.45 GHz wasapplied with a power of 600 W. At the same time the externalelectromagnet 12 applied a diverging magnetic field of 1500 Gauss at themicrowave introducing window 11, 875 Gauss at the exit of the plasmachamber and 650 Gauss at the base material. Also a negative bias of -500V was applied to the mold base by a bias source (not shown), and a DLCfilm of a thickness of 1500 Å was formed. In this operation, the moldbase was heated to 300° C. A molding test as in the example 7, employingthus obtained mold, provided results similar to those in the example 7.

Embodiment of effecting ion implantation during or after carbon filmformation (examples 14-23)!

(EXAMPLE 14)

FIGS. 1 and 2 also illustrate an embodiment of the mold of the presentinvention for optical element formation. FIG. 1 shows the state of thepress molding surface for the optical element while FIG. 2 shows a stateafter the molding. In this embodiment, a numeral 2 in FIG. 1 indicatesan a-C:H film subjected to ion beam mixing, constituting the moldingsurface for molding an optical element.

The mold of the present invention for the optical element will now beexplained in detail as follows.

A mold base was obtained by working sintered SiC into a predeterminedshape, then forming a polycrystalline SiC film by CVD mirror-polishingthe molding surface. After sufficient washing, the mold base materialwas placed in the IBD apparatus shown in FIG. 8, and an a-C:H film wasformed with a thickness of 1500 Å. After the vacuum tank was evacuatedto 10⁻⁶ Torr, Ar gas was introduced at 20 sccm from the gas inlet intothe ionizing chamber and was ionized. An ion beam was extracted byapplying a voltage of 500 V to the ion beam extracting grid, therebyirradiating the mold base for 10 minutes and thus cleaning the moldingsurface thereof. Subsequently, CH₄ at 16 sccm and H₂ at 32 sccm wereintroduced into the ionizing chamber, and the a-C:H film was formed witha thickness of 1500 Å under a gas pressure of 4.5×10⁻⁴ Torr. Then, in anunrepresented ion implanting apparatus, C⁺¹² obtained by mass separationwas implanted into the a-C:H film with an energy of 50 keV and aconcentration of 1×10¹⁷ ion/cm². The surface roughness of the moldingsurface after the ion implantation was evaluated as R_(max) =0.03 μm.

The thus obtained mold was employed in a molding operation as in theexmaple 1, in the molding apparatus shown in FIG. 4. In the observationsunder an optical microscope and a scanning electron microscope, the moldafter moldings 300 times did not show defects such as scars or cracks,nor Pb precipitation resulting from reduction of PbO contained in theglass, nor glass fusion. Also, the molded products were satisfactory inthe surface roughness, surface precision, transmittance and shapeprecision, and were free from Pb precipitation or gas retention.

The mold was also used in a molding operation similar to that of theexample 1, utilizing the molding apparatus shown in FIG. 6. Even aftermoldings of 3000 times the surface roughness of the molding surface ofthe mold and of the molded optical element, and the releasing propertyof the mold from the molded optical element were evaluated assatisfactory. Also, in the observations under an optical microscope anda scanning electron microscope, the molding surface did not show defectssuch as scars or cracks, nor Pb precipitation nor glass fusion.

(EXAMPLE 15)

A base material was obtained by working a sintered material consistingof WC (84%), TiC (8%) and TaC (8%) into a predetermined shape, andmirror-polishing the molding surface to R_(max) =0.02 μm. The mold basematerial was placed in the sputtering apparatus shown in FIG. 10, andthe spontaneous oxide film on the surface of the mold base waseliminated by reverse Ar sputtering. More specifically, after the vacuumtank 160 was evacuated to 1×10⁻⁶ Torr by the evacuating system 163, Argas was introduced to a pressure of 1×10⁻³ Torr from the gas supplysystem 162, and a high frequency voltage of 13.56 MHz was applied fromthe RF power source 164 to sputter the mold base material. Then, incontinuation, sputtering was conducted with a graphite target 165 of apurity of 99.99% and with Ar plasma to form a hard carbon film of athickness of 500 Å on the molding surface. The sputtering was conductedwith a gas pressure of 3×10⁻³ Torr and an applied RF power density of 6W/cm². The mold base was then placed in a composite IBD apparatus shownin FIG. 12, wherein shown are a mold base and a holder 166 therefor, ahigh energy ion source 167 for mixing, a low energy ion source 168 forforming an a-C:H film, and an evaporation source 169 consisting of anelectron gun. The ion sources 167, 168 are basically same in structureas in the IBD appratus employed in the example 14. At first, the moldbase was opposed to the ion source 167, then CH₄ and H₂ were introducedand ionized in the source 167, and ion implantation was conducted withan energy of 50 keV and a concentration of 6×10⁻¹⁶ ion/cm².Subsequently, an a-C:H film of a thickness of 1500 Å was formed with theion source 168 under the same conditions as in the example 14.

Thus obtained mold was used in the molding apparatus shown in FIG. 4,for molding flint optical glass SF14 (softening point Sp=586° C.;transition temperature Tg=485° C.) 300 times as in the example 14.

In the observations under an optical microscope or a scanning electronmicroscope, the mold after the molding operations did not show defectssuch as scars or cracks, nor precipitation resulting from reduction ofPbO contained in the glass, nor glass fusion. Also, the molded productswere satisfactory in the surface roughness, surface precision,transmittance and shape precision, and were free from Pb precipitationor gas retention.

(EXAMPLE 16)

The mold base of the example 15 was placed in the ECR-PCVD apparatusshown in FIG. 3 and was subjected to the formation of a DLC film of athickness of 1000 Å. More specifically, after the apparatus wasevacuated to 1×10⁻⁶ Torr, C₆ H₆ was introduced from the gas supplysystem at 35 sccm to a pressure of 3.0×10⁻³ Torr, and microwave of 2.45GHz was applied by the oscillator 8 with a power of 700 W. At the sametime the external electromagnet 12 applied a diverging magnet field of1500 Gauss at the microwave introducing window, 875 Gauss at the exit ofthe plasma chamber, and 650 Gauss at the position of the mold base, andan RF bias of 500 V was applied to the mold base. Then, elements shownin Table 4 were implanted as in the example 14 by an unrepresented ionimplantation apparatus. Subsequently, flint optical glass SF 14(softening point Sp=586° C.; transition temperature Tg=485° C.) wasmolded 300 times in the same manner as in the example 4 with the moldingapparatus shown in FIG. 4. The obtained results are also shown in Table4.

                  TABLE 4                                                         ______________________________________                                                            Amount of                                                      Ele-   Energy  implantation                                                                          Releasing                                         Mold ment   (kev)   (ion/cm.sup.2)                                                                        property                                                                              Durability of mold                        ______________________________________                                        1    C       50     9 × 10.sup.13                                                                   glass fusion                                                                          film peeled after                                                             moldings 100 times                        2    C       50     1 × 10.sup.14                                                                   satisfactory                                                                          no peeling after                                                              moldings 300 times                        3    Ne     110     5 × 10.sup.14                                                                   satisfactory                                                                          no peeling after                                                              moldings 300 times                        4    Ar     110     5 × 10.sup.14                                                                   satisfactory                                                                          no peeling after                                                              moldings 300 times                        5    Xe     110     2 × 10.sup.15                                                                   satisfactory                                                                          no peeling after                                                              moldings 300 times                        6    Kr     110     2 × 10.sup.15                                                                   satisfactory                                                                          no peeling after                                                              moldings 390 times                        7    N      120     1 × 10.sup.17                                                                   satisfactory                                                                          no peeling after                                                              moldings 300 times                        8    O      120     1 × 10.sup.16                                                                   satisfactory                                                                          no peeling after                                                              moldings 300 times                        9    H      120     7 × 10.sup.17                                                                   satisfactory                                                                          no peeling after                                                              moldings 300 times                        10   He     120     7 × 10.sup.17                                                                   satisfactory                                                                          no peeling after                                                              moldings 300 times                        11   C      100     2 × 10.sup.18                                                                   satisfactory                                                                          no peeling after                                                              moldings 300 times                        ______________________________________                                    

(EXAMPLE 17)

A mold base on which a DLC film was formed under the same conditions asin the example 16 was placed in the IBD apparatus of the example 15, andwas subjected to the implantation of N with an energy of 100 keV and aconcentration of 1×10¹⁷ ion/cm² by the high energy ion source. Then, incontinuation, an a-H:C film of a thickness of 1500 Å was formed by thelow energy ion source. A molding test as in the example 14, employingthus obtained mold, provided results similar to those of the example 14.

(EXAMPLE 18)

The mold base of the example 15 was placed, after sufficient washing, inthe film forming apparatus shown in FIG. 12. After the apparatus wasevacuated to 1×10⁻⁷ Torr, Ar gas was introduced into the low energy ionsource with a pressure of 1×10⁻³ Torr, the oxide film present on thesurface of the mold base was eliminated by 500 Å by Ar ion beam etching.In continuation, an a-C:H film of a thickness of 2500 Å was formed byeffecting the formation of the a-C:H film with the low energy ion sourceand simultaneously irradiating C ions of an energy of 40 keV with thehigh energy ion source. A molding test as in the example 14, employingthus obtained mold, provided results similar to those of the example 14.

(EXAMPLE 19)

In the formation of the a-C:H film in the process of the example 18, thehigh energy ion source irradiated N ions of 40 keV, instead of C ions,for initial 5 minutes from the start of film formation, and then thefilm formation was continued with the low energy ion source only,thereby obtaining a film of 3000 Å. A molding test as in the example 14,employing thus obtained mold, provided reresults similar to those in theexample 14.

(EXAMPLE 20)

A mold base was prepared by working sintered Si₃ N₄ into a predeterminedshape, and mirror-polishing said material to a surface roughness ofR_(max) =0.03 μm. This mold base was placed in the composite IBDapparatus shown in FIG. 12, and, after the vacuum tank was evacuated to1×10⁻⁶ Torr, a Si film of a thickness of 500 Å was formed with theelectron gun 169, under a pressure of 1×10⁻⁵ Torr. Then, an a-C:H filmof a thickness of 5000 Å was formed by the low energy ion source, withsimultaneous irradiation of C ions of 50 keV by the high energy ionsource under the same conditions as in the example 18. A molding test asin the example 14, employing thus obtained mold, provided resultssimilar to those in the example 14.

(EXAMPLE 21)

A mold base same as in the example 15 was placed in an ion beamsputtering apparatus shown in FIG. 13, provided with a vacuum tank 190,a sputtering ion source 191, an irradiating ion source 192, a sputteringtarget 193, a mold and a holder 194, and an evacuating system 195. Afterthe apparatus was evacuated to 1×10⁻⁶ Torr, Ar ions from the sputteringion source 184 were extracted with a voltage of 0.7 kV to irradiate thegraphite target 186 of a purity of 99.99%, thereby effecting sputteringon the mold 187 to form a hard carbon film thereon. At the same time theion source 185 irradiated N ions, of 40 keV, thereby obtaining a film ofa thickness of 3000 Å. This operation was conducted with a temperatureof base material of 300° C., and a pressure of 2.5×10⁻¹⁴ Torr. A moldingtest as in the example 14, employing thus obtained mold, providedresults similar to those of the example 14.

(EXAMPLE 22)

A mold base same as in the example 14 was placed in a composite IBDapparatus provided with an ECR ion source and an ion irradiating Kaufmanion source, as shown in FIG. 14. In this drawing there are shown avacuum tank 196, an ECR ion source 197, an ion irradiating Kaufman ionsource 198, a mold and a holder 199, an evacuating system 200, and anelectron gun 201. After the apparatus is evacuated to 1×10⁻⁶ Torr, C₆ H₆was introduced at 40 sccm into the ECR ion source, to a pressure of4.5×10⁻³ Torr. Then, microwave of 2.45 GHz was applied by the oscillatorand the wave guide with a power of 700 W, and an RF bias of 500 V wasapplied to the mold base, whereby a DLC film was formed with a thicknessof 2500 Å. The film formation was conducted with simultaneousirradiation of N ions of 50 keV by the Kaufman ion source. A moldingtest as in the example 14, employing the thus obtained mold, providedresults similar to those of the example 14.

(EXAMPLE 23)

After the surfacial oxide film of the mold base was removed as in theexample 18, graphite of a purity of 99.99% was evaporated with theelectron gun shown in FIG. 12, and a mixture of N:He=7:3 was introducedat 20 sccm to the low energy ion source to effect an assistingirradiation with an ion beam of 200 eV and 4 mA. At the same timeirradiation of C ions of 50 keV was conducted for 10 minutes by the highenergy ion source. The graphite evaporation and the N ion irradiationwere continued after the irradiation of C ions was terminated, therebyforming a diamond film of a thickness of 1 μm. Since the film had asurface roughness of R_(max) =0.03 μm, it was employed in the moldingoperation without mechanical polishing. A molding test as in the example14, employing the mold, provided results similar to those in the example14.

As explained in the foregoing, the first mold of the present invention,for forming an optical element, having a carbon film such as a diamondfilm, a DLC film, an a-H:C film or a hard carbon film at least on themolding surface of a mold base, is provided at the interface between thecarbon film and the mold base with an area in which a constituentelement of the mold base and a constituent element of the film arebonded to oxygen. Thus, there is obtained a molding mirror surface thathas little defects and does not generate film peeling or cracks in theglass molding.

The second mold of the present invention, for forming an opticalelement, is subjected to carbon ion injection at least on the moldingsurface of a mold base, or to such carbon ion injection followed by theformation of a carbon film such as a diamond film, a DLC film, an a-H:Cfilm or a hard carbon film. Thus, there is obtained a molding mirrorsurface that has little defects and does not generate film peeling orcracks in the glass molding.

The third mold of the present invention, for forming an optical element,is subjected during or after the formation of a carbon film such as adiamond film, a DLC film, an a-H:C film or a hard carbon film at leaston the molding surface of a mold base to the injection of ions of a highenergy having a flying path larger than the film interface preferablywith a concentration of 10⁻¹⁴ ion/cm² or higher, in order to mix theatoms of the mold base and the film at the interface thereof, therebyinducing elimination of the sharp interface or formation of a compoundby atom mixing, thus achieving significant improvement in the adhesionstrength of the film and the mold base. Thus, there is obtained amolding mirror surface that has little defects and does not generatefilm peeling or cracks in the glass molding.

Such molds, when employed in the molding of the optical elements, showextremely satisfactory releasing property from the molded glass, andalso can provide molded products satisfactory in the surface roughness,surface precision, transmittance and shape precision. Also such moldsare extremely durable without defects such as film peeling, cracks orscars even when the press molding operation is repeated for a prolongedperiod.

Thus, the mold of the present invention for forming the optical elementcan achieve improvement in the productivity and reduction in the cost.

What is claimed is:
 1. A mold for press molding an optical element ofglass, wherein carbon ions are injected into a molding surface of a moldbase of said mold and wherein said molding surface subjected to saidcarbon ion injection is subjected to further treatment in order to formon said molding surface a film selected from the group consisting of adiamond film, a hydrogenated amorphous carbon film, and a hard carbonfilm or a film consisting of a mixture of at least two thereof.
 2. Amold according to claim 1, wherein said molding surface subjected tosaid carbon ion injection is heat treated, and is subjected to saidfurther treatment in order to form on said molding surface said filmselected from the group consisting of a diamond film, a hydrogenatedamorphous carbon film, and a hard carbon film or a film consisting of amixture of at least two thereof.
 3. A mold according to claim 1, whereinsaid molding surface subjected to said carbon ion injection is heattreated, then irradiated with hydrogen plasma and subjected to saidfurther treatment in order to form on said molding surface said filmselected from the group consisting of a diamond film, a hydrogenatedamorphous carbon film, and a hard carbon film or a film consisting of amixture of at least two thereof.
 4. A mold according to claim 1, whereinan amount of said carbon ion injection is within a range of 10¹⁵ to 10¹⁸ion/cm².